1. Field of the Invention
The present invention relates to a control device and a gait generating device for a bipedal mobile robot.
2. Description of the Related Art
For a bipedal mobile robot, such as a humanoid robot, which has two legs connected to the body thereof through the intermediary of joints, a technique for causing a robot to travel by carrying out a series of motions of each leg leaving from a floor and then landing on the floor (hereinafter referred to simply as “the motion of leaving from/landing on a floor” in some cases), alternating between two legs, (i.e., by performing a walking motion or a running motion of the robot) has conventionally been proposed by the applicant of the present application, as disclosed in, for example, Japanese Patent No. 3674788.
Although the aforesaid motion of leaving from/landing on a floor performed by alternating between the two legs is a typical type of the motions of the two legs required in a bipedal mobile robot, the type of motions is not limited thereto. For example, there is a case where a bipedal mobile robot preferably performs a single or a plurality of motions of only one leg leaving from/landing on a floor while the other leg of the two legs is off the floor in order to prevent the posture of the robot from being disturbed when, for example, a lateral external force acts on the robot due to contact or the like between the robot and an object (hereinafter referred to “the one-leg hopping motion in some cases). It is also possible that the robot carries out the one-leg hopping motion as necessary in response to, for example, a request by an operator of the robot.
Meanwhile, a bipedal mobile robot usually has a laterally symmetrical construction. Hence, when the robot performs the aforesaid motion of leaving from/landing on a floor motion, alternating between its two legs (when the robot carries out a walking motion or a running motion), the body (base body) of the robot as observed in a lateral plane (frontal plane) is normally maintained at a posture when the robot stands straight or a posture close thereto (a posture in which the body trunk of the body as observed in the lateral plane is substantially vertical).
However, the study conducted by the inventors of the present application has revealed that, when the robot performs the aforesaid one-leg hopping motion, an attempt to maintain the body of the robot at the same posture as that in a walking motion or a running motion leads to an inconvenience described below.
In the case where a bipedal mobile robot is operated to carry out the aforesaid one-legged hopping motion, the total center-of-gravity point of the robot is preferably positioned substantially right above the ground contact surface of the one leg in a state wherein the one leg carrying out the motion of leaving from/landing on a floor has landed on a floor after leaving from the floor.
In this case, if the body trunk axis of the body of the robot as observed in the lateral plane is oriented substantially in the vertical direction (if the posture of the body is the aforesaid upright posture or close thereto), then the position of the proximal end portion (the portion connected to the body) of the one leg on the floor would be dislocated in a lateral direction from the position right above the aforesaid ground contact surface of the one leg. This is because, in the bipedal mobile robot having the laterally symmetrical construction, the total center-of-gravity point of the robot in the state wherein the body trunk axis of the robot body is oriented substantially in the vertical direction lies in the vicinity of the middle between the proximal end portions of the two legs in the transverse direction (the lateral direction) of the robot.
Therefore, especially in the period immediately after the one leg lands on the floor after leaving from the floor, a relatively large moment acts about an axis in the longitudinal direction (about a roll axis) of the robot on the joint of the proximal end portion of the one leg due to the gravitational force acting on the robot and the inertial force in the vertical direction (i.e., due to a floor reaction force that balances out the resultant force of the gravitational force and the inertial force).
This inconveniently results in an increased size or weight of the joint of the proximal end portion of the one leg or an actuator driving the joint.